Rotary pump or motor with an axially rotating rotor

ABSTRACT

The specification discloses a rotary helical gear pump having a stator formed with at least one helical gear and a rotor mounted therein formed with at least one helical gear meshing therewith, the number of starts of the gear or gears and the stator differing by one from that of the rotor. A flexible drive shaft is secured to the rotor in one of a number of different ways, to drive the rotor, the drive shaft being coated with a nonpermeable and nonporous layer, which is effectively sealed to the rotor, to reduce the effects of corrosion fatigue.

United States Patent ROTARY PUMP OR MOTOR WITH AN AXIALLY ROTATING ROTOR5 Claims, 6 Drawing Figs.

US. Cl 418/48, 418/179 Int. Cl F01c U10, 7 F010 5/00, F046 1/06 Field ofSearch 103/117 M;

[56] References Cited UNITED STATES PATENTS 2,463,341 3/1949 Wade 418/482,502,512 4/1950 Demetriades 287/53 R 3,242,130 3/1966 Jackopin 106/143,479,960 11/1969 Cardoso 418/48 FOREIGN PATENTS 223,042 8/1962 Austria418/48 Primary Examiner-Carlton R. Croyle Assistant Examiner.lohn J.Vrablik AttorneyCushman, Darby & Cushman ABSTRACT: The specificationdiscloses a rotary helical gear pump having a stator formed with atleast one helical gear and a rotor mounted therein formed with at leastone helical gear meshing therewith, the number of starts of the gear orgears and the stator differing by one from that of the rotor. A flexibledrive shaft is secured to the rotor in one of a number of differentways, to drive the rotor, the drive shaft being coated with anonpermeabie and nonporous layer, which is effectively sealed to therotor, to reduce the efiects of corrosion fatigue.

ROTARY PUMP OR MOTOR WITH AN AXIALLY ROTATING ROTOR The presentinvention relates to a rotary pump or motor with an eccenuicallyrotating rotor. One particular form of such pump is a helical gear pumpwhich includes a stator provided with one or more internal helical gearsor teeth, and a rotor provided with one or more external helical gearsor teeth, meshing with those of the stator, the number of starts of thegear or gears of one member being one more than that of the othermember. With such pumps, the rotor executes a rotary motion, and alsoorbits in either the same sense or the opposite sense as the rotarymotion. Other forms of such pumps or motor are those of the Wankel typein which the rotor again executes a rotary action and an orbitingmotion.

In the helical gear pump, the rotor is conventionally connected to adrive motor by an intermediate drive shaft, provided at each end with auniversal joint, the universal joints accommodating both the rotary andthe orbiting motion. Since these pumps are often used to pump corrosiveliquids or powders, the universal joint, particularly at the rotor endof the drive-shaft, is subject to considerable wear and leaching of thejoint lubricant.

According to the present invention there is provided a rotary pump ormotor comprising a stator having a rotor eccentrically rotatable withrespect thereto, a flexible drive shaft secured to the rotor to drivethe rotor or receive drive therefrom, the flexible drive shaft beingcoated with a nonpermeable and nonporous layer. The invention alsoprovides a rotary helical gear pump comprising a stator formed with atleast one helical gear, a rotor formed with at least one helical gearmeshing with the stator gear or gears, the number of starts of the gearor gears of the stator differing by one from the number of starts of thegear or gears of the rotor, and a flexible drive shaft secured to therotor to drive the rotor, such shaft being coated with a nonpermeableand nonporous layer. Preferably, such a coating layer should be capableof flexing, and be sufficiently tough to permit handling and withstandabrasion.

It will be appreciated that the flexible shaft will be subject to asubstantial cyclic stress variation. By providing the coating ofnonpermeable and nonporous material, the effect of corrosion fatigue iseliminated, the shaft itself being only likely to fail under normalfatigue conditions.

While a few stainless steels have a high resistance to fatigue in thepresence of corrosive'or reactive media such as atmospheric aircontaining moisture or water, these stainless materials are extremelycostly and, in any event, are not entirely free from fatigue. Byproviding a coating of nonpermeable and nonporous material, it ispossible to use a steel of moderate strength which is comparativelycheap and readily obtainable.

Suitable coating materials include a plastics material known under thetrade name Penton, which is a chlorinated polyether, which is preferred,nitral rubber and certain epoxy resins.- A thin coating of gold alsoprovides good results from a corrosion fatigue point of view, but itsrelative softness makes it liable to abrasion in certain uses of a pump.Penton" can be applied to the flexible shaft using a fluidized bedtechnique whilecertain epoxy resins have the advantage that they cansimply be painted on. Generally, it is not possible to plate a coatingonto the shaft, since such a process tends to induce certain tensilestresses in the shaft, which can affect the latters fatigue resistance.

In order that the invention may more readily be understood, thefollowing description is given, merely by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a fragmentary scrap section, which is showing a helical gearpump rotor into which is fitted the end of a flexible shaft, accordingto the present invention;

FIG. 2 is a similar view showing a second method of fixing a coatedflexible shaft to the rotor, the view being in half section;

FIGS. 3 and 4 are views similar to FIG. 2 of two further methods offixing the flexible shaft to the rotor, and

FIGS. 5 and 6 show a cross section of the complete pumps of FIGS. 1 and2 respectively to a smaller scale.

In the embodiment illustrated in FIGS. 1 and 5 a helical gear pump isshown as comprising a resilient stator 10 mounted in a housing 11 andhaving a helically threaded bore 12, the thread having one more or oneless start than that of the helically threaded rotor 13. In order todrive the rotor 13 in its rotating and orbiting path, a drive shaft 14is secured thereto. This drive shaft comprises an elongate steel member15 provided at each end with an enlargement 16. The connection to therotor is shown in greater detail in FIG. 1, and a similar connection iseffected at the other end of the flexible drive shaft where it isconnected to a key shaft (FIG. 5) which may be secured to the armatureshaft of an electric motor (not shown).

To the left of the enlargement, as seen in FIG. 1, the shaft 14 isprovided with an outwardly stepped portion 17, followed by areduced-diameter portion 18 which is formed with a thread 19 whichengages a corresponding thread formed in a bore 20 in the rotor 13.

Surrounding the shaft 15 is a coating 21 of a chlorinated polyetherplastics material sold under the trade name Penton. This coating can beapplied by the fluidized bed technique, and is applied on that portionof the shaft 15 between the step 17, and the corresponding step at theother end of the shaft. Before the shaft is threaded into the rotor, thecoating 21 is of a thickness which is slightly greater than the depth ofthe step 17. Thus, when the shaft is threaded into the bore 20 of therotor 13, the portion 22 adjacent the step is compressed against acountersunk portion or countersink 23 at the mouth of the bore 20.

The compression by the countersunk portion 23 of the coating 21 ensuresthe fluidtight seal between the rotor and the shaft, and prevents anyliquid or other material being pumped from attacking the threadedportion of the shaft 15. In each of the four embodiments of pumpdescribed in the present specification, the shaft 15 is approximately 60inches long and 0.75 inch in diameter over the majority of its length.For other sizes of pumps, the porportions of the shaft will be much thesame while the actual dimensions may be larger or smaller. Theseproportions permit the shaft to flex sufficiently to allow for theeccentricity of the rotor. It will be apparent that considerablevariations in stress will occur as the shaft rotates, but the coating orlayer 21 serves to prevent corrosion fatigue causing failure of theshaft 15.

The method of securing the shaft 14 at the right-hand end, as indicatedabove, is similar. As can be seen in FIG. 5, a key shaft 100 is boltedto a hollow shaft 101 which is mounted for rotation in the housing 102by means of bearings 103 and 104, a seal between the shaft 101 and thehousing 102 being effected by a suitable packing ring located between agland 106 and a gland ring 107. In FIG. 5 the inlet to the pump isillustrated at 108 and the outlet at 109.

The embodiment of FIG. 1 has the advantage that it can be manufacturedcheaply and readily, but it does also have the disadvantage thatrotation may only be performed in one direction, since rotation in theopposite direction will tend to unscrew the thread 19 from thecorresponding thread in the stator 13. In the other three embodimentsthis problem does not arise. In the construction of FIGS. 2 and 6, thepump includes a stator 24 and the rotor 25 as before, but in thisembodiment the rotor is provided with an axial enlarged bore 26 whichextends a substantial distance therethrough. At its lefthand end, asseen in FIG. 2, the bore 26 communicates with a tapered bore 27, theangle of which is such as to form a morse taper, to bores 26 and 27extending through the complete length of the rotor. Engaged in thistaper is the correspondingly tapered head 28 of a drive shaft 29 whichis again provided with a coating 30 of plastics material. This coating30 extends into an annular groove 31, in which is also seated an O-ring32 which, together with the coating which engages in the taper 27provides a seal between the shaft 29 and the rotor 25. In order toprevent the shaft 29 from disengaging from the taper 27 a locking bolt33 engages in a threaded bore or recess 34 in the shaft 29, the head 35of the bolt bearing against the end of the rotor. The complete pump isillustrated in FIG. 6, in which like parts have been given likereference numerals to those of FIG. 5, with the addition of the letterA.

The modified embodiment illustrated in FIG. 3 includes a resilientstator 36 and a rotor 37 formed with an axial bore 38 similar to thebore 26 of the FIG. 2 embodiment. A drive shaft 39 is of a generallysimilar shape to the drive shaft 14 of FIG. 1 and is provided with anenlargement 40 and a step 41, a plastics material coating 42 ending atthe step 41. The shaft 39 is provided with a right-hand screw thread 43,which is screwed into a corresponding thread in a bore 44, and is alsoprovided with an extension having a left-hand screw thread 45 whichextends on a portion of the shaft beyond the end of the rotor 37. As inFIG. 1, the coating extends beyond the enlargement and engages against acountersink where the bore 44 meets the bore 38. Screwed onto the thread45 is a cap locknut 46 having a groove 47, in the one end face whichaccommodates a sealing O-ring 48, which bears against the end face ofthe rotor 37, to seal the drive shaft from external material.

A generally similar arrangement is shown in FIG. 4, and like parts havebeen given like reference numerals, with the addition of the letter B.In this embodiment, instead of having a cap locknut 46, the drive shaft398 is itself formed with a threaded bore or recess 50 having aleft-hand thread 51 formed therein into which engages the thread of alock bolt 52, the head of which bears against the end of the rotor 378.

We claim:

1. A rotary helical gear pump comprising, in combination:

i. a stator formed with at least one helical gear;

ii. a rotor formed with at least one helical gear meshing with saidstator gear or gears, the number of starts to said gear or gears of saidstator differing by one from the number of starts of said gear or gearsof said rotor;

iii. an axial bore formed in said rotor and having a circumscribing walltherearound;

iv. a key shaft having an axial bore formed therein and a circumscribingwall therearound;

v. a solid flexible unitary drive shaft having a rotor-driving endengaged in said bore of said rotor and a driven end and a sealingportion axially inward of said driving end and said driven end;

vi. a first enlargement to said drive shaft axially inward of said rotordriving end and a second enlargement to said drive shaft axially inwardof said driven end;

vii. a nonpermeable and nonporous corrosion-fatigue-resistant layercoating said drive shaft, portions of said layer overlying said firstand second enlargements, said portions of said layer engaging betweensaid drive shaft enlargementsand said rotor and said key shaft to sealsaid drive shaft against contact with fluid to the exterior of the driveshaft; and

viii. cooperating thread means on said rotor and said drive shaft and onsaid key shaft and said drive shaft effective to urge said portions ofsaid coating into contact with said rotor and said key shaftrespectively.

2. A pump as specified in claim 1, wherein said layer is formed ofchlorinated polyether, nitral rubber or an epoxy resin.

3. A pump as specified in claim 1, wherein said axial bore is threaded,said pump further comprising a countersink to said threaded bore, athreaded end to said drive shaft engaged in said threaded bore, one ofsaid portions of said layer engaging between said enlargement and saidcountersink to seal the said drive shaft.

4. A pump as specified in claim 1, wherein said axial bore is threadedwith a thread of one hand, said pump further comprising an enlarged borein said rotor communicating with said threaded bore, said enlarged boreand said threaded bore together extending through the full length of therotor, a countersink to said threaded bore at the junction thereof withsaid enlarged bore, a threaded end to said flexible drive shaft, with athread of said one hand, engaged in said threaded bore, said drive shaftextending through and beyond said enlarged bore, one of said portions ofsaid layer engaging between said en largements and said countersink toseal the said drive shaft.

5. A pump as specified in claim 4, further comprising a threadedextension beyond said threaded end, having a thread of the opposite handto said one hand, and a locknut, lockingly engaged on said threadedextension.

1. A rotary helical gear pump comprising, in combination: i. a statorformed with at least one helical gear; ii. a rotor formed with at leastone helical gear meshing with said stator gear or gears, the number ofstarts to said gear or gears of said stator differing by one from thenumber of starts of said gear or gears of said rotor; iii. an axial boreformed in said rotor and having a circumScribing wall therearound; iv. akey shaft having an axial bore formed therein and a circumscribing walltherearound; v. a solid flexible unitary drive shaft having arotor-driving end engaged in said bore of said rotor and a driven endand a sealing portion axially inward of said driving end and said drivenend; vi. a first enlargement to said drive shaft axially inward of saidrotor driving end and a second enlargement to said drive shaft axiallyinward of said driven end; vii. a nonpermeable and nonporouscorrosion-fatigue-resistant layer coating said drive shaft, portions ofsaid layer overlying said first and second enlargements, said portionsof said layer engaging between said drive shaft enlargements and saidrotor and said key shaft to seal said drive shaft against contact withfluid to the exterior of the drive shaft; and viii. cooperating threadmeans on said rotor and said drive shaft and on said key shaft and saiddrive shaft effective to urge said portions of said coating into contactwith said rotor and said key shaft respectively.
 2. A pump as specifiedin claim 1, wherein said layer is formed of chlorinated polyether,nitral rubber or an epoxy resin.
 3. A pump as specified in claim 1,wherein said axial bore is threaded, said pump further comprising acountersink to said threaded bore, a threaded end to said drive shaftengaged in said threaded bore, one of said portions of said layerengaging between said enlargement and said countersink to seal the saiddrive shaft.
 4. A pump as specified in claim 1, wherein said axial boreis threaded with a thread of one hand, said pump further comprising anenlarged bore in said rotor communicating with said threaded bore, saidenlarged bore and said threaded bore together extending through the fulllength of the rotor, a countersink to said threaded bore at the junctionthereof with said enlarged bore, a threaded end to said flexible driveshaft, with a thread of said one hand, engaged in said threaded bore,said drive shaft extending through and beyond said enlarged bore, one ofsaid portions of said layer engaging between said enlargements and saidcountersink to seal the said drive shaft.
 5. A pump as specified inclaim 4, further comprising a threaded extension beyond said threadedend, having a thread of the opposite hand to said one hand, and alocknut, lockingly engaged on said threaded extension.